Ok, so nostr:npub1493l95wrel6a6r2wnylf0gtx5na50n5uew55jka09nzv2lda806qa5vtzu (which I use to host Bitcoin Explained) is doing something in their HTML that Mastodon parses in order to produce an inline player.

nostr:npub1v5ufyh4lkeslgxxcclg8f0hzazhaw7rsrhvfquxzm2fk64c72hps45n0v5 should do that too, cc nostr:npub1unmftuzmkpdjxyj4en8r63cm34uuvjn9hnxqz3nz6fls7l5jzzfqtvd0j2.